KR101078136B1 - Aqueous acidic immersion plating solutions and methods for plating on aluminum and aluminum alloys - Google Patents

Abstract

The present invention provides a bisyanide acidic aqueous solution for immersion plating having a pH of about 3.5 to about 6.5 and comprising zinc ions, nickel ions, and / or cobalt iron ions, and fluoride ions. In one embodiment, the immersion plating solution of the present invention further comprises one or more nitrogen atoms, sulfur atoms, or both nitrogen and sulfur atoms. The present invention also relates to a method for depositing a zinc-alloy coating on aluminum and aluminum lower substrate, including immersing an aluminum or aluminum alloy substrate in the bisyanide acidic aqueous solution for immersion plating of the present invention. Optionally, the zinc alloy coated aluminum or aluminum alloy substrate is plated using an electroless or electrolytic metal plating solution.

Description

Acid solution for immersion plating, and plating method on aluminum and aluminum alloy {AQUEOUS ACIDIC IMMERSION PLATING SOLUTIONS AND METHODS FOR PLATING ON ALUMINUM AND ALUMINUM ALLOYS}

The present invention relates to an acidic aqueous solution for immersion plating and a method for depositing a zinc alloy protective coating on an aluminum or aluminum alloy substrate. The invention also relates to a metal plated aluminum or aluminum alloy substrate.

One of the fastest growing markets in the metal finishing / electroplating industry is the processing and plating of aluminum and its alloys. The unique physical and mechanical properties of aluminum, together with the decoration field, are particularly useful in industries such as automotive, electronics, telecommunications and avionics. Among the most interesting properties of aluminum are low overall density (2.7 g / cc), high mechanical strength achieved through alloying and heat treatment, and its relatively high corrosion resistance. Additional properties of aluminum include high thermal and electrical conductivity, magnetic neutrality, high scrap value, and amphoteric chemical properties thereof. Aluminum articles for many applications are made from various aluminum alloys using elements for alloys including silicon, magnesium, copper and the like. Such alloy mixtures are formed to achieve enhanced properties such as high strength or ductility.

Plating of aluminum and its alloys requires specific surface formulations for successful electrolytic and electroless deposition. The most common practice used to achieve successful electrodeposition is to apply an immersion zinc coating (also better known as zincate) to the substrate immediately before plating. This procedure has long been regarded as the most economical and practical method of aluminum pretreatment. The main advantages of applying the zincate layer for pretreatment are the relatively low cost of equipment and chemicals, a wider operating window for processing, and the ease of applying controlled deposits.

The presence of other metals in the zincate solution affects the zinc deposition rate and its efficiency. Small amounts of alloying components (ie Fe, Ni, Cu) not only improve the adhesion of the zincate deposition layer but also increase the usefulness of the zincate for various aluminum alloys. For example, the addition of Fe ions enhances adhesion to magnesium containing alloys. The presence of nickel in the zincate enhances the adhesion of nickel plated directly onto the zincite and a similar effect can be found in the copper plate after adding copper to the zincate. In general, however, the alloy of the jinkate provides a thinner and more compact deposition layer, which is effectively interpreted as a good bond to subsequent electroless / electrolytic plating. On the other hand, the composition of the alloy zincate is further complicated by the additional metal ions in the composition. This complicates the choice of complexing agent and is important for the overall performance of the ginkect. Zinc-iron-nickel compositions are more sensitive than zinc-iron compositions to the selection of complexing agents and ratios of metal ions in the composition. This becomes even more important with the addition of copper ions in the alloy zincate. Due to the important phase in the galvanic series, the deposition ratio of copper in immersion jincate deposition is much higher than other elements in the jincate. Therefore, control of the deposition rate of copper becomes important. The deposition rate of copper can be controlled by the selection of suitable complexing agents for copper ions and suitable ratios with other metal ions. There are a few strong complexing agents for copper ions, which provide the excellent stability and performance of alloying zincates, and cyanide appears to be the best candidate. Cyanide is chosen as a complexing agent for copper containing zincate compositions and has been the industry standard material for this use for many years. A negative aspect of the use of cyanide is that cyanide has extremely toxic properties, and as with other metal finishing products, research to replace cyanide in alloying ginklets has long been of interest.

In recent years there have been several noncyanide-based alloy zincate compositions that have been developed, but these compositions still contain hard complexing agents such as EDTA, NTA, ethylene diamine, etc., to maintain the multi-ion system in a stable form. Not only does it have to be disposed of, it also makes cleaning more difficult. In addition, the zincate treatment generally performs better under multiple treatment forms. Aluminum pretreatment by single immersion in the zincate does not yield as good results as a double or triple immersion process in the zincite prior to the subsequent plating step. Such multiple gating processes require more processing steps and time, which means that they are more complex, less productive and less economical. Thus, the research for replacing conventional alkaline cyanide-based or cyanide-based alloying zincates for plating on aluminum like other metal finishing products has been a subject of interest in recent years.

Summary of the Invention

The present invention relates to bisyanide based immersion plating comprising zinc ions, nickel ions and / or cobalt ions, fluoride ions, and optionally one or more inhibitors containing one or more nitrogen atoms, sulfur atoms, or both nitrogen and sulfur atoms. Provide an acidic aqueous solution. In addition, the present invention, after the aluminum or aluminum base alloy is immersed in the acidic solution for immersion plating of the present invention to deposit a zinc alloy protective coating, and optionally zinc-coated aluminum or aluminum using an electroless or electrolytic metal plating solution A method of depositing a zinc alloy protective coating on aluminum and aluminum base alloys, including plating an alloy substrate.

In one embodiment, the present invention relates to an acidic aqueous solution for immersion plating that does not contain cyanide ions, and in particular, a cyanide-based acid for immersion plating useful for depositing a zinc alloy protective coating on aluminum and various aluminum based alloy substrates. It relates to an aqueous solution. Thus, in one embodiment, the non-cyanide acidic aqueous solution for immersion plating of the present invention has a pH of about 3.5 to about 6.5, and includes zinc ions, nickel and / or cobalt ions, and fluoride ions, but cyanide ions It does not contain. In another embodiment, the acidic aqueous solution for immersion plating of the present invention may contain other metal ions such as copper ions, iron ions, manganese ions and zirconium ions and / or one or more metal complexing agents. In another embodiment, the solution may also contain one or more inhibitors containing one or more nitrogen atoms, sulfur atoms, or both nitrogen and sulfur atoms.

The acidic aqueous solution for immersion plating of the present invention can be produced by dissolving a water-soluble salt of a preferred metal in water. Examples of the source of zinc ions in the immersion plating solution include zinc fluoride, zinc nitrate, zinc chloride, zinc sulfate, zinc acetate and the like.

Nickel ions can be introduced into an acidic aqueous solution for immersion plating by dissolving nickel salts such as nickel acetate, nickel nitrate, nickel sulfate and the like. Cobalt ions can be introduced as cobalt acetate, cobalt nitrate, cobalt sulfate, and the like. Iron salts useful for introducing selective iron ions include ferrous chloride, ferric chloride, ferrous sulfate, ferric sulfate, ferrous nitrate, ferric nitrate and the like. Copper ions can be introduced by dissolving salts such as cuprous chloride, cuprous nitrate, cupric nitrate, cupric chloride, cuprous sulfate, cupric sulfate and the like in water. Other metal ions can be introduced by dissolving salts such as manganese (II) chloride, manganese (II) sulfate, zirconium chloride, magnesium chloride, magnesium sulfate and the like.

In one embodiment, the acidic aqueous solution for immersion plating contains nickel ions but no cobalt ions. In another embodiment, the acidic aqueous solution for dip plating contains nickel ions and cobalt ions. In another embodiment, the acidic aqueous solution for immersion plating contains cobalt ions but no nickel ions. For economic reasons, the acidic aqueous solution for immersion plating contains nickel ions or a mixture of nickel and a small amount of cobalt. In one embodiment, the concentration of nickel ions or cobalt ions or a mixture of cobalt ions and nickel ions is higher than the concentration of zinc ions.

The acidic aqueous solution for immersion plating of the present invention also contains fluoride ions. The source of fluoride ions can be any soluble fluoride compound so long as the ions introduced with the fluoride ions do not adversely affect the performance of the solution. Metal or ammonium fluoride may be used. Typical fluoride materials include hydrofluoric acid, alkali metal or ammonium fluorides such as sodium fluoride, ammonium fluoride and the like, and alkali metal or ammonium bifluorides such as sodium fluoride, ammonium bifluoride (ammonium bifluoride) and the like. . Since high solubility is desired whenever possible, highly soluble fluorides such as sodium or ammonium bifluoride are preferred. In one embodiment, the acidic aqueous solution for immersion plating contains from about 0.005 to about 100 g / l of fluoride ions.

The acidic aqueous solution for immersion plating of the present invention has a pH in the range of about 3.5 to about 6.5. In another embodiment, the pH of the solution can range from about 4.0 to about 6.0, and in yet another embodiment, the pH of the solution ranges from about 4.5 to about 5.5.

In one embodiment, the acidic aqueous solution for immersion plating of the present invention

About 1 to about 150 g / l zinc ions,

About 5 to about 250 g / l nickel and / or cobalt ions, and

And from about 0.005 to about 0.05 g / l of fluoride ions.

In another embodiment, the acidic aqueous solution for immersion plating of the present invention

About 10 to about 30 g / l zinc ions,

About 20 to about 50 g / l nickel and / or cobalt ions, and

About 0.5 to about 10 g / l of fluoride ions.

In one embodiment, the concentration of zinc ions is lower than the concentration of nickel and / or cobalt ions.

The acidic aqueous solution for immersion plating of the present invention may also contain one or more inhibitors containing one or more nitrogen atoms, one or more sulfur atoms, or both nitrogen and sulfur atoms. In one embodiment, such nitrogen atoms are not present in aliphatic amines or hydroxylamines. In another embodiment, the acidic aqueous solution for dip plating of the present invention also contains one or more metal complexing agents. Such solutions provide improved stability of the complexing system and acceptable performance for various aluminum and aluminum alloys. The acidic aqueous solution for immersion plating of the present invention does not contain cyanide ions, and this solution provides additional advantages of environmentally friendly applications for the pretreatment of various metal substrates such as aluminum and aluminum base alloys. In another embodiment, the acidic aqueous solution for dip plating of the present invention does not contain a hard complexing agent comprising an aliphatic amine such as EDTA, NTA, ethylenediamine, and the like.

Inhibitors useful in the acidic aqueous solution for immersion plating of the present invention can be selected from a wide variety of compositions containing nitrogen and / or sulfur atoms. Thus, in one embodiment, the inhibitor can be selected from one or more compounds represented by the formula:

R ₂ NC (S) Y (I)

Where

Each R is independently hydrogen or an alkyl, alkenyl or aryl group,

Y is XR ¹ , NR ₂ or N (H) NR ₂ , where X is O or S and R ¹ is hydrogen or an alkali metal. Examples of such compounds include thiourea, thiocarbamate and thiosemicarbazide.

Thiourea compounds that can be used in the present invention can be represented by the formula:

[R ₂ N] ₂ CS (II)

Where

Each R is independently hydrogen or an alkyl, cycloalkyl, alkenyl or aryl group.

Alkyl, cycloalkyl, alkenyl and aryl groups may contain up to 10 or more carbon atoms and substituents such as hydroxy, amino and / or halogen groups. Alkyl and alkenyl groups can be straight or branched. Thioureas used in the present invention include thiourea or various technically recognized derivatives, homologs or analogs thereof. Examples of such thioureas include thiourea, 1,3-dimethyl-2-thiourea, 1,3-dibutyl-2-thiourea, 1,3-didecyl-2-thiourea, 1,3-di Ethyl-2-thiourea, 1,1-diethyl-2-thiourea, 1,3-diheptyl-2-thiourea, 1,1-diphenyl-2-thiourea, 1-ethyl-1- ( 1-naphthyl) -2-thiourea, 1-ethyl-1-phenyl-2-thiourea, 1-ethyl-3-phenyl-2-thiourea, 1-phenyl-2-thiourea, 1,3- Diphenyl-2-thiourea, 1,1,3,3-tetramethyl-2-thiourea, 1-allyl-2-thiourea, 3-allyl-1,1-diethyl-2-thiourea and 1 -Methyl-3-hydroxyethyl-2-thiourea, 2,4-dithiobiuret, 2,4,6-trithiobiuret, alkoxy ether of isothiourea and the like.

Thiocarbamates which can be used as inhibitors in the acidic aqueous solution for immersion plating of the present invention include thiocarbamates represented by the formula:

R ₂ NC (S) -XR ¹ (III)

Where

Each R is independently hydrogen or an alkyl, alkenyl or aryl group,

X is O or S,

R ¹ is hydrogen or an alkali metal.

Alkyl and alkenyl groups may contain about 1 to about 5 carbon atoms. In other embodiments, the alkyl group may contain 1 or 2 carbon atoms each. In another embodiment, the R groups are all alkyl groups containing one or two carbon atoms. Examples of such thiocarbamates include dimethyl dithiocarbamic acid, diethyl dithiocarbamic acid, sodium dimethyldithiocarbamate hydrate, sodium diethyldithiocarbamate trihydrate, and the like.

Thiosemicarbazide, which may be used as an inhibitor in the acidic aqueous solution for immersion plating of the present invention, includes thiosemicarbazide represented by the following formula:

R ₂ NC (S) -N (H) NR ₂ (IV)

Where

Each R is independently hydrogen or an alkyl, alkenyl or aryl group.

In one embodiment, the R group is an alkyl group containing 1 to 5 carbon atoms, and in other embodiments the alkyl group may each contain 1 or 2 carbon atoms. Examples of such thiosemicarbazide include 4,4-dimethyl-3-thiosemicarbazide and 4,4-diethyl-3- thiosemicarbazide.

In addition, the acidic aqueous solution for immersion plating of the present invention may contain, as an inhibitor, one or more nitrogen-containing disulfides represented by the following formula:

[R ₂ NCS ₂ ] ₂ (V)

Where

Each R is independently hydrogen or an alkyl, alkenyl or aryl group.

In one embodiment, the R group may contain 1 to 5 carbon atoms. In other embodiments, the alkyl group may contain 1 or 2 carbon atoms each. In another embodiment, the R groups are all alkyl groups containing one or two carbon atoms. Examples of such organic disulfides include bis (dimethylthiocarbamyl) disulfide (tiram), bis (diethylthiocarbamyl) disulfide and the like.

In addition, inhibitors useful in the present invention may be nitrogen containing heterocyclic compounds which may be substituted or unsubstituted.

Examples of the substituent include alkyl group, aryl group, nitro group, mercapto group and the like. Nitrogen-containing heterocyclic compounds may contain one or more nitrogen atoms, and examples of such nitrogen-containing heterocyclic compounds include pyrrole, imidazole, benzimidazole, pyrazole, pyridine, dipyridyl, piperazine, Pyrazine, piperidine, triazole, benzotriazole, tetrazole, pyrimidine and the like. Nitrogen-containing heterocyclic compounds may also contain other atoms such as oxygen or sulfur. Examples of heterocyclic compounds containing nitrogen and oxygen are morpholines, and examples of nitrogen-containing heterocyclic compounds containing nitrogen and sulfur are thiazoles, thiazolins and thiazolidines.

In one embodiment, the inhibitor comprises one or more of the above-described nitrogen-containing heterocyclic compounds substituted with mercapto groups. Specific examples of mercapto substituted nitrogen-containing heterocyclic compounds useful as inhibitors in the immersion plating solution of the present invention include 2-mercapto-1-methyl imidazole; 2-mercaptobenzimidazole; 2-mercaptoimidazole; 2-mercapto-5-methyl benzimidazole; 2-mercaptopyridine; 4-mercaptopyridine; 2-mercaptopyrimidine (2-thiouracil); 2-mercapto-5-methyl-1,4-thiadiazole; 3-mercapto-4-methyl-4H-1,2,4-triazole; 2-mercaptothiazoline; 2-mercaptobenzothiazole; 4-hydroxy-2-mercaptopyrimidine; 2-mercaptobenzoxazole; 5-mercapto-1-methyltetrazole; And 2-mercapto-5-nitrobenzimidazole.

Inhibitors useful in the immersion plating solution of the present invention may also include alkali metal thiocyanates such as sodium thiocyanate and potassium thiocyanate. Thioalcohols and thioacids may also be included as inhibitors in the immersion plating solution of the present invention. Examples of such inhibitors include 3-mercapto ethanol; 6-mercapto-1-hexanol; 3-mercapto-1,2-propanediol; 1-mercapto-2-propanol; 3-mercapto-1-propanol; Mercaptoacetic acid; 4-mercaptobenzoic acid; 2-mercaptopropionic acid; And 3-mercaptopropionic acid.

In one embodiment, the immersion plating solution of the present invention may contain one or more of the inhibitors described above. In another embodiment, the immersion plating solution contains two or more inhibitors described above. When included in the immersion plating solution, the amount of inhibitor may vary from about 0.0005 to about 5 g / l or more, and in yet other embodiments, this amount may vary from about 0.005 to about 0.05 g / l. In one embodiment, the amount of inhibitor may vary from about 0.005 to about 100 g / l.

The dip plating solution of the present invention may also contain one or more metal complexing agents. Complexing agents are useful for dissolving metal ions in the plating solution. The amount of complexing agent included in the plating solution of the present invention may be about 5 to about 250 grams or more per liter. In one embodiment, the concentration of complexing agent (s) is about 20 to about 100 g / l. Useful complexing agents can be selected from many kinds of materials including those containing anions such as acetates, citrates, glycolates, lactates, maleates, pyrophosphates, tartrates, gluconates, glucoheptonates and the like. Mixtures of two or more complexing agents can be used in the immersion plating solution of the present invention. Specific examples of the complexing agent include sodium tartrate, sodium acetate, disodium tartrate, sodium gluconate, potassium gluconate, potassium acid tartrate, sodium potassium tartrate (Rochelle salt), and the like.

Metal complexing agents that may be included in the immersion plating solution of the present invention may also include, in some embodiments, aliphatic amines, aliphatic hydroxylamines, or mixtures thereof. In another embodiment, the complexing agent comprises a mixture of one or more aliphatic amines and / or aliphatic hydroxylamines and one or more other complexing agents described above. The amount of amine included in the immersion plating solution of the present invention may vary from about 1 to about 50 g / l. Examples of useful amines are ethylenediamine, diaminopropane, diaminobutane, N, N, N, N-tetramethyldiaminomethane, diethylenetriamine, 3,3-aminobispropylamine, triethylene tetramine, mono Ethanolamine, diethanolamine, triethylanolamine, N-methyl hydroxylamine, 3-amino-1-propanol, N-methyl ethanolamine and the like. In another embodiment, the immersion plating solution of the present invention is free of aliphatic amines and aliphatic hydroxylamine.

The acidic aqueous solution for dip plating of the present invention can be prepared by dissolving the various components mentioned above in water. The components may be mixed with water in any order. Organic acids such as acetic acid, lactic acid and the like can be included in the plating solution to adjust the pH of the solution.

The following examples illustrate the acidic aqueous solution for immersion plating of the present invention. All parts and percentages are by weight, temperature is in degrees Celsius, and pressure is at or near atmospheric unless otherwise indicated elsewhere in the following examples or described description and / or claims.

TABLE 1

Example A-H

Solution Example ^* A B C D E F G H Zinc Acetate 2H ₂ O 30 30 30 30 30 30 30 30 Nickel Acetate 4H ₂ 0 30 70 70 70 70 70 70 70 Cobalt Acetate 4H ₂ O - - - - - - - Ammonium bifluoride One 3 3 3 3 3 3 3 2-mercaptobenzothiazole 0.01 - - 2,2'-dipyridyl 0.01 - - 1,3-diethyl-2-thiourea 0.01 - 2-benzimidazole 0.01 2-mercapto-1-methylimidazole 0.01 1,10-phenanthroline 0.01 pH 5.5 5.5 5.5 5.5 5.5 5.5 5.5 5.5

^* All parts are g / l and the rest is water

Table 2

Example I-M

Solution Example ^* I J K L M Zinc Acetate 2H ₂ O 38 38 45 40 35 Nickel Acetate 4H ₂ 0 75 75 100 75 - Cobalt Acetate 4H ₂ O 75 Ammonium bifluoride 4 4 5 4 3 2-mercaptobenzothiazole 0.005 0.005 0.005 0.005 2,2'-dipyridyl 1,3-diethyl-2-thiourea 0.005 0.005 2-benzimidazole 2-mercapto-1-methylimidazole 0.005 0.005 1,10-phenanthroline pH 5.0 5.0 5.0 5.0 5.0

^* All parts are g / l and the rest is water

The bisyanide-based acid solution for immersion plating of the present invention described above is useful for depositing a zinc alloy protective coating as a pretreatment agent for aluminum and various alloys of aluminum. In one embodiment, improved results are obtained when the plating solution contains one or more of the inhibitors described above. It is believed that the use of the inhibitors described above in the immersion plating solution, and combinations of inhibitors and complexing agents, at least partially improves the performance of the immersion plating solution of the present invention. Inhibitors affect zinc alloy deposition rates and create even thinner coatings on aluminum and aluminum alloys. Using the dip plating solutions described herein, a coating weight of zinc alloy protective of about 2-6 mg / ft ² can be obtained.

In addition to aluminum, the immersion plating solution of the present invention is useful for depositing zinc alloy protective coatings on a variety of aluminum alloys, including both cast and wrought alloys. Examples of cast alloys are 356, 380 and 383 alloys. Examples of forged alloys are aluminum alloys of the type 1100, 2024, 3003, 3105, 5052, 5056, 6061, 6063 and 7075.

In one embodiment, depositing a zinc alloy protective coating using the acidic solution for dip plating of the present invention comprises pretreatment of an optional metal plating of an aluminum or aluminum alloy substrate using an electroless or electrolytic metal plating solution. Implementation is included. It should be understood that water cleaning is generally applied after each process step.

The first step of an optional pretreatment process is to wash any grease, dirt or oil on the aluminum surface using, for example, a suitable alkaline, acidic or solvent, non etch cleaner. Suitable cleaners include nonsilicated weak alkaline cleaners and silicified weak alkaline cleaners, both of which are used for about 1 to about 5 minutes at a temperature of about 49 to 66 ° C. After cleaning, aluminum is generally washed with water.

The etching of the cleaned aluminum substrate is then carried out using conventional etchant which may be acidic or alkaline. Generally acidic etchant is used. In one embodiment, the etching solution may contain 50% nitric acid. In the process used in the examples below, the etching solution used to remove excess oxide from the aluminum surface is Alklean AC-2 (5% volume) from Atotech, USA, which The solution comprises phosphoric acid / sulfuric acid / fluoride. The aluminum or aluminum alloy is contacted with Alkyne AC-2 at about 20-25 ° C. for about 1-2 minutes. The etched sample is then washed with water.

The etched aluminum surface is then desmuted. The dematting process is a process of removing excessive dust from the surface of aluminum. The dismating process can be carried out using a nitric acid solution (eg 50 vol% solution) or a mixture of nitric acid and sulfuric acid. In one embodiment, a conventional discoloring solution for aluminum alloys may contain 25 wt% sulfuric acid, 50 wt% nitric acid, and 25 wt% ammonium fluoride. The dismatting process can also be carried out with a mixture of nitric acid and sulfuric acid containing acidic, fluoride salt products containing ammonium bifluoride. In the examples below, the etched aluminum alloy was de-flavored for about 1 minute at a temperature of about 20-25 ° C. using NF (100 g / L), DeSmutter from Atotech USA, and washed with water. Dismater NF comprises a mixture of acid salts and persulfate-based oxidants.

For complete application of the aluminum substrate, the aluminum substrate is immersed in the bisyanide-based acidic solution for immersion plating of the present invention for a short time such as about 100 to about 150 seconds, so that the zinc alloy protective coating is etched on the etched and discolored aluminum substrate. Apply. The temperature of the immersion plating solution is generally maintained between about 20 to 25 ° C. Excess immersion plating solution is generally removed from the aluminum substrate surface by water washing with deionized water. In the examples below, aluminum is immersed in the indicated dip plating solution at 20-25 ° C. for about 120-150 seconds.

Following the acidic immersion plating treatment described above, the zinc alloy coated aluminum substrate may be plated with any suitable metal using electroless or electrolytic plating processes well known in the art. Suitable metals include nickel, copper, bronze, brass, silver, gold and platinum. In one embodiment, the zinc alloy coated aluminum substrate is plated by an electroless nickel or electrolytic plating process such as sulfamate nickel strike or copper pyrophosphate strike solution.

Examples 1-14 below illustrate metal plating after depositing a zinc alloy protective coating according to the invention on various aluminum alloys. Test plaques of aluminum alloys with a thickness of 0.09 to 0.25 inch, 1 inch wide and 4 inch long were used for the plating test. All test plaques were cleaned, etched and discolored as described above prior to soaking in the bisyanide based acidic solution for immersion plating of the present invention. The metal layer was plated up to about 1 millimeter or slightly thicker prior to the adhesion test. In Examples 1-13, zinc alloy coated samples were plated with nickel at about 95 ° C. for 90 minutes using a Nichem-2500 (Atotech, USA) electroless nickel bath. In Example 14, a zinc alloy coated sample was electrolytically plated in a copper pyrophosphate electroplating solution at about 25 ASF current density for 45 minutes. The zinc alloy coated sample of Example 15 was plated in a sulfamate nickel electrolytic strike bath followed by polished copper acid, polished nickel and decorative chromium electroplating steps. The metal plated samples of Examples 1-15 were then washed with water, dried and tested for adhesion of nickel or other plated metal to the aluminum substrate. Adhesion of the plated metals was measured using one or more of the following tests. One adhesion test included the use of a 90 ° bend. In this test, the plated sample was bent at 90 ° and then the inner and outer surfaces of the bent area were examined for lift-off (scale) of the plated metal from the base aluminum substrate. The adhesion of the plated metals was evaluated as follows: good (0% lift-off), titration (less than 10% lift-off on either side of the bent area) and poor (greater than 20% lift-off) . For casting alloys, the "Reverse Saw", "Grinding" and "Scribe / Cross-Hatch" methods are used to investigate the adhesion of the plated metal, The criteria were used to evaluate adhesion. Several plated samples were also tested after baking at 150 ° C. for 2 hours and quenched in cold water (20 ° C.), after which the plated surfaces were subjected to “no swell / pass” and “swell / s) / failure criteria. The swelling phenomenon was analyzed.

Example 1-10

Zinc alloy coatings were deposited on forged aluminum alloys 2024 and 6061 using immersion plating solutions of Examples A-K and M. The zinc alloy coated aluminum alloy was then plated at about 95 ° C. for 90 minutes in a Nichem-2500 (Atotech USA) electroless nickel bath. Plated samples were washed with water, dried and tested for adhesion using the 90 ° bending test described above. The results are summarized in Table 3 below.

TABLE 3

90 ° bending adhesion test results

Example Example
Immersion plating solution 2024 alloy 6061 alloy One A Good / good proper 2 B Good proper 3 C Good Good 4 D Good proper 5 E Good Good 6 F Good Good 7 G Good Good 8 H Good proper 9 I Good proper 10 J Good Good 11 K Good Good 12 M Good Good

Example 13

Aluminum alloys including forging alloys including casting alloys 356 and 380, and 1100, 2024, 3003, 5052, 6061, and 7075, were coated with zinc alloy using the immersion plating solution of Example L followed by electroless nickel plating. . Nickel-plated portions were tested for adhesion in a 90 ° bending test, and in grinding and cold water quenching methods. All samples were rated good.

Example 14

Aluminum alloys 2024 and 6061 were coated using the immersion plating solution of Example L by the method described above. The zinc alloy coated sample was then electrolytically plated in a copper pyrophosphate bath at about 25 ASF current density for 45 minutes. Copper plated samples were tested for adhesion of plated copper to aluminum alloys and no adhesion failure was recognized in the 90 ° bending test.

Example 15

The method of Example 14 was repeated except that the zinc alloy coated portion was plated in a sulfamate nickel electrolytic strike bath followed by a polished copper acid, polished nickel and decorative chromium electroplating step. This electroplated sample was tested for adhesion using the 90 ° bending test and the baking test described above. No adhesion loss or swelling on the plated surface was observed on any plated sample.

Example 16

The method of Example 15 was repeated except that the zinc alloy coating was deposited using the immersion plating solution of Example M. No adhesion loss or swelling on the plated surface was observed in any plated sample.

While the present invention has been described in terms of various embodiments, it should be understood that other variations thereof will be apparent to those skilled in the art having the benefit of this specification. It is, therefore, to be understood that the invention described herein is intended to cover such modifications as fall within the scope of the appended claims.

Claims (49)

A method of depositing a zinc alloy protective coating on an aluminum or aluminum based alloy substrate, the method comprising: (A) An aluminum or aluminum based alloy substrate having a pH of 4.5 to 5.5 and for affecting the deposition rate of zinc ions and both nickel ions or cobalt ions or both nickel and cobalt ions, fluoride ions, and zinc alloys Immersion plating the aluminum or aluminum based alloy substrate by immersion plating in an acidic aqueous solution for immersion plating containing one or more inhibitors and containing no cyanide ions for a time sufficient to deposit the desired coating; And (B) removing the coated substrate from the acidic aqueous solution for immersion plating; Wherein said at least one inhibitor is a mercapto substituted nitrogen-containing heterocyclic compound wherein acetate is provided as a counter ion to zinc ions and nickel ions or cobalt ions or both nickel and cobalt ions. The method of claim 1, wherein the surface of the aluminum or aluminum based alloy is cleaned, etched and demutated before immersing in a solution for immersion plating. The method of claim 2, wherein the cleaning is performed using an alkaline cleaner, an acid cleaner, or a solvent cleaner, and the etching is performed using an alkaline etching or acid etching solution. 3. The method of claim 2 wherein the aluminum or aluminum base alloy is subjected to each step of cleaning, etching, dematting, and immersion plating, followed by washing with water. The method of claim 1 wherein the plating solution further contains one or more metal complexing agents. The method of claim 5, wherein the metal complexing agent is selected from acetate, citrate, glycolate, lactate, maleate, pyrophosphate, tartrate, gluconate, or glucoheptonate, and mixtures thereof. The method of claim 1, wherein the plating solution further contains one or more additional metal ions selected from copper ions, iron ions, manganese ions, magnesium ions, and zirconium ions. The method of claim 1, wherein the mercapto substituted nitrogen-containing heterocyclic compound is selected from thiazoles, thiazolins, and thiazolidines. The method of claim 1 wherein the plating solution contains 1 to 150 g / l of zinc ions and 5 to 250 g / l of nickel ions or cobalt ions or both nickel and cobalt ions. The method of claim 1 wherein the plating solution contains 0.0005 to 5 g / l of inhibitor. The method of claim 1 wherein the plating solution is free of aliphatic amines and aliphatic hydroxylamine. The method of claim 1 wherein the solution comprises 0.5 to 10 g / l fluoride ions. A method of depositing a zinc alloy protective coating on an aluminum or aluminum based alloy substrate, the method comprising: (A) An aluminum or aluminum based alloy substrate having a pH of 4.5 to 5.5 and 10 to 30 g / l of zinc ions, and 20 to 50 g / l of nickel or cobalt ions or both nickel and cobalt ions, 0.5 Sufficient to deposit the desired coating in an acidic aqueous solution for immersion plating comprising from 10 to 10 g / l fluoride ions and at least 0.005 to 0.05 g / l at least one inhibitor to affect the deposition rate of the zinc alloy. Immersion plating the substrate by immersion plating for a time; And (B) removing the coated substrate from the acidic aqueous solution for immersion plating; Wherein said at least one inhibitor is a mercapto substituted nitrogen-containing heterocyclic compound wherein acetate is provided as a counter ion to zinc ions and nickel ions or cobalt ions or both nickel and cobalt ions. The method of claim 13, wherein the surface of the substrate is cleaned, etched, and descented prior to immersion in the immersion plating solution. The method of claim 14, wherein the cleaning is performed using an alkaline cleaner, an acid cleaner, or a solvent cleaner, and the etching is performed using an alkaline etching or acid etching solution. 15. The method of claim 14, wherein the substrate is washed with water after each step of the cleaning, etching, dismatizing and immersion plating steps. The method of claim 13, wherein the plating solution further contains 1 to 250 g / l of one or more metal complexing agents. The method of claim 17, wherein the metal complexing agent is selected from acetate, citrate, glycolate, lactate, maleate, pyrophosphate, tartrate, gluconate, or glucoheptonate, and mixtures thereof. The method of claim 13, wherein the mercapto substituted nitrogen-containing heterocyclic compound is selected from thiazoles, thiazolins, and thiazolidines. The method of claim 13, wherein no aliphatic amine and aliphatic hydroxylamine are present in the plating solution. The method of claim 13, wherein the plating solution further comprises one or more metal ions selected from copper ions, iron ions, manganese ions, magnesium ions, and zirconium ions. A method of depositing a zinc alloy protective coating on an aluminum or aluminum based alloy substrate, the method comprising: (A) An aluminum or aluminum based alloy substrate having a pH of 4.5 to 5.5 and for affecting the deposition rate of zinc ions and both nickel ions or cobalt ions or both nickel and cobalt ions, fluoride ions, and zinc alloys Applying an immersion zinc alloy protective coating on a substrate by immersion plating in an acidic aqueous solution for immersion plating containing one or more inhibitors and containing no cyanide ions for a time sufficient to deposit the desired coating; And (B) plating the zinc alloy coated substrate using an electroless or electrolytic metal plating solution, Wherein said at least one inhibitor is a mercapto substituted nitrogen-containing heterocyclic compound wherein acetate is provided as a counter ion to zinc ions and nickel ions or cobalt ions or both nickel and cobalt ions. 23. The method of claim 22, wherein the surface of the substrate is cleaned, etched and discolored before immersing in a solution for immersion plating. The method of claim 23, wherein the cleaning is performed using an alkaline cleaner, an acid cleaner or a solvent cleaner, and the etching is performed using an alkaline etching or acid etching solution. 24. The method of claim 23, wherein the aluminum or aluminum base alloy is subjected to each step of cleaning, etching, dematting, and immersion plating, followed by washing with water. 23. The method of claim 22, wherein the plating solution contains 1 to 150 g / l zinc ions and 5 to 250 g / l nickel ions or cobalt ions or both nickel and cobalt ions. The method of claim 22, wherein the plating solution contains 0.0005 to 5 g / l of inhibitor. The method of claim 22, wherein the plating solution further contains 1 to 250 g / l of one or more metal complexing agents. The method of claim 28, wherein the metal complexing agent is selected from acetate, citrate, glycolate, lactate, maleate, pyrophosphate, tartrate, gluconate, or glucoheptonate, and mixtures thereof. 23. The method of claim 22, wherein the mercapto substituted nitrogen-containing heterocyclic compound is selected from thiazoles, thiazolins, and thiazolidines. 23. The method of claim 22, wherein no aliphatic amine and aliphatic hydroxylamine are present in the plating solution. The method of claim 22, wherein the plating solution further comprises one or more metal ions selected from copper ions, iron ions, manganese ions, magnesium ions, and zirconium ions. The method of claim 22, wherein the solution comprises 0.5 to 10 g / l fluoride ions. A method of depositing a zinc alloy protective coating on an aluminum or aluminum based alloy substrate, the method comprising: (A) An aluminum or aluminum based alloy substrate has a pH of 4.5 to 5.5 and a zinc ion of 1 to 150 g / l, 5 to 250 g / l of nickel ions or cobalt ions or both nickel and cobalt ions, 0.005 to In an acidic aqueous solution for immersion plating containing 100 g / l of fluoride ions and at least 0.005 to 100 g / l of at least one inhibitor for influencing the deposition rate of the zinc alloy and free of cyanide solution, Immersing the substrate by immersion plating for a time sufficient to deposit the coating; And (B) removing the coated substrate from the acidic aqueous solution for immersion plating; Wherein said at least one inhibitor is a mercapto substituted nitrogen-containing heterocyclic compound and wherein acetate is provided as a counter ion to zinc ions and nickel ions or cobalt ions or both nickel and cobalt ions. 35. The method of claim 34, wherein the plating solution further contains one or more metal complexing agents. 36. The method of claim 35, wherein the metal complexing agent is selected from acetate, citrate, glycolate, lactate, maleate, pyrophosphate, tartrate, gluconate, or glucoheptonate, and mixtures thereof. 35. The method of claim 34, wherein the mercapto substituted nitrogen-containing heterocyclic compound is selected from thiazoles, thiazolins, and thiazolidines. 35. The method of claim 34, wherein the plating solution further contains one or more metal ions selected from copper ions, iron ions, manganese ions, magnesium ions, and zirconium ions. 35. The method of claim 34, wherein no aliphatic amine and aliphatic hydroxylamine are present in the plating solution. 35. The method of claim 34, wherein the surface of the aluminum or aluminum base alloy is cleaned, etched and discolored before immersing in a solution for immersion plating. 41. The method of claim 40, wherein the cleaning is performed using an alkaline cleaner, an acid cleaner, or a solvent cleaner, and the etching is performed using an alkaline etching or acid etching solution. 41. The method of claim 40, wherein the aluminum or aluminum base alloy is subjected to each step of cleaning, etching, dematting, and immersion plating, followed by washing with water. delete delete delete delete delete delete delete